The invention relates to a vehicle engine control device having a driver-operated engine operation preset control element and a speed regulation and/or limitation stage which regulates or limits the vehicle travelling speed, using an engine-power-related nominal preset signal and emitting an engine-power-related control signal (DE 44 39 424 C1).
Various versions of such vehicle engine control devices are known. The engine operation preset control element is used by the driver to influence engine operation in a desired manner; that is, to demand a desired engine operating state. Traditionally, this control element is an accelerator pedal, which can be deflected by the driver and whose deflection represents the engine operating state desired by the driver. In the most widely used, conventional system type, as is traditionally used in motor vehicle internal combustion engines having a throttle valve, the accelerator pedal deflection is interpreted as demanding a corresponding setting for the throttle valve position, and thus as an engine-power-related setting signal, for example in the form of the classical mechanical coupling between the accelerator pedal and the throttle valve. Speed regulation units and speed limiting units, such as those which have been introduced by the Applicant under the designations Tempomat(trademark) and Speedtronic(trademark), operate on this basis at the throttle valve position preset level. They are thus related to engine power, in that they are supplied with the accelerator pedal position information as an engine-power-related nominal preset signal and they emit an engine-power-related control signal for regulating the throttle valve position and, possibly, other engine power parameters, in particular the fuel injection parameters, in such a way that the speed of travel is regulated or limited at a desired nominal value. One example of such an apparatus is disclosed in German Patent Document DE 37 10 891 A1. Another speed regulation system of this conventional type, which is particularly suitable for Otto-cycle or diesel engines with injection, is described in German Patent Document DE 44 39 424 C1, which has already been cited above.
This conventional regulation and/or limiting of the speed of travel at the throttle valve position level, and thus at the engine power level, has a self-stabilizing effect. This is because, as the rotation speed increases, the amount of combustion air with which the cylinder is filled is reduced, so that the engine torque decreases and, in consequence, the power is reduced. When the rotation speed decreases, on the other hand, the cylinder filling, and thus the engine torque, increase, and in consequence the engine power rises. With this response, the engine thus automatically acts in the same sense for regulation or limiting of the speed of travel in the sense of negative feedback, in that the engine torque setting is reduced when the vehicle goes too fast, while the engine torque is increased when the vehicle goes too slow.
Since the speed of travel can be linked to the engine rotation speed via the circumference of the vehicle wheels and via the axle and transmission step-up ratios, regulation and limiting systems for the vehicle speed are, in the final analysis, rotation speed regulation systems and limiting systems, respectively. In consequence, presetting a desired nominal or limiting speed is equivalent to presetting a corresponding, constant engine rotation speed, which means that in the classical throttle-valve-position-related systems, the throttle valve position, and thus the engine torque as a dependent variable, are set in proportion to the speed control error, with the entire adjustment range being available. The clear association between the control signal emitted from the regulation or limiting system for the desired engine power is thus provided.
Recently, vehicle engine control devices have become of increasing interest which operate at the engine torque level, that is to say with a torque structure. This means that the setting of the engine operation preset control element, for example an accelerator pedal, is assessed as a driver demand for a specific engine torque, and not on for a specific throttle valve position or engine power. In these engine controllers, which have recently become of increasing interest, based on an engine torque preset, an appropriate throttle valve position or an equivalent engine power parameter for the driver""s demand, as expressed by him by operation of the engine operation preset control element, is determined only at the end of the engine control action chain, generally on the basis of a suitable engine model. The operation of the engine operation preset control element thus no longer has any direct effect on the throttle valve position, which term, in the following text, also refers to any other, equivalent engine power parameter, particularly in the case of an engine without a throttle valve.
This has exacerbating effects for systems where the speed of travel is regulated and/or limited automatically, because a constant torque preset can be associated with arbitrary engine rotation speeds over wide ranges. If, now, the engine is intended to maintain a specific rotation speed for the present torque preset, for example because the resistance to movement is not forcing any reduction in speed, then this can lead to the vehicle speed being in an unacceptably wide range for precise speed regulation. Furthermore, a constant torque preset means that, in the event of an increase in rotation speed which would result in the torque being reduced, the torque reduction is compensated for by continuous opening of the throttle valve in order to maintain the torque preset. Even though the vehicle speed is increasing, the throttle valve is thus opened further, so that, in the speed regulation system, the control error is first of all increased; that is, there is a positive-feedback effect in the positive direction. Analogously, there is a positive-feedback effect in the negative direction when the rotation speed decreases, in which case the torque would be reduced. But this is compensated for by continuous closure of the throttle valve in order to maintain the torque preset; that is, the throttle valve is closed further even through the vehicle is slowing down, so that the control error of the speed regulation system is once again increased. Thus, without any further actions, the engine in such engine control systems based on torque automatically acts in the opposite sense to conventional regulation and/or limiting of the speed of travel on a throttle valve position or engine power basis, thus not ensuring stable speed regulation or limiting.
In a motor vehicle described in European Patent Document EP 0 299 235 A2 and having a speed regulation device, operation of the accelerator pedal is interpreted as presetting a desired speed of travel.
One object of the invention is to provide a vehicle engine control apparatus of the type mentioned initially which operates at the torque level, and also allows satisfactory regulation and/or limitation of the speed of travel.
This and other objects and advantages are achieved by the control arrangement according to the invention, in which a torque characteristic stage is provided, which emits an engine-torque-related nominal preset signal as a function of the operation of the engine operation preset control element, normally an accelerator pedal. The engine operating state demand expressed by the driver on the control element is in this way interpreted as a torque demand; that is, the engine control system operates on a torque basis, and forms a torque structure. A conventional speed regulation or speed limiting stage operates at the throttle valve position level (that is, the engine power level).
Characteristically, the input side of the speed regulation or speed limiting stage has an associated torque/power characteristic stage, which transforms the engine-torque-related nominal preset signal, produced by the torque characteristic stage from the engine operation preset control element signal, into an appropriate nominal preset signal which is related to the engine power, and is thus related to the throttle valve position. The latter signal can then be processed in a conventional manner by the subsequent speed regulation stage or speed limiting stage, which operates at the throttle valve position level, and thus at the engine power level. In a corresponding way, the output side of the speed regulation or speed limiting stage has an associated power/torque characteristic stage, which corresponds to the inverse of the torque/power characteristic stage on the input side. The power/torque characteristic stage is used to transform the control signal emitted from the speed regulation or speed limiting stage at the throttle valve position level (that is, the engine power level) into a control signal at the engine torque level.
Thus, overall, a speed regulation and/or speed limiting stage which operates in a conventional manner at the engine power level is embedded at a suitable point in the torque structure of an engine control system operating at the engine torque level. Although embedding this behind the torque characteristic stage involves the use of the torque/power characteristic stage and the power/torque characteristic stage, this allows the destabilizing characteristics of the downstream engine control action chain to be taken into account correctively in its characteristics. Furthermore, in consequence, the action chain of the speed regulation or speed limiting stage remains decoupled from the application of an accelerator pedal characteristic which determines the driving characteristics, so that any change in these driving characteristics does not affect any previous application of the speed regulation or speed limiting stage and, in consequence, interactive relationships are avoided.
It is furthermore advantageous that the extremely well-proven, conventional regulator and limiter structures, which operate at the engine power level, can be transferred unchanged to the speed regulation stage and the speed limiting stage, irrespective of the type of air control used by the engine, and irrespective of what variable is used as the regulated variable when the engine torque does not represent the suitable regulated variable. Furthermore, the torque structure of the engine control system can be designed and optimized entirely on the basis of engine factors, without the speed regulation and limiting placing any limitations on this. The path gain of the control path for regulating or limiting the speed is the same as that at the throttle valve position level, which is higher than at the torque level, irrespective of the type of regulator.
One embodiment of the invention includes not only speed regulation but also speed limiting in parallel therewith; and maximum and minimum selection units are provided in a suitable way on the output side of the speed regulation stage and the speed limiting stage, respectively. The maximum selection unit allows the speed regulation to be overwritten by corresponding driver operation of the engine operation preset control element, while the minimum selection unit ensures that a selected limiting speed is not overshot.
Another embodiment of the invention also includes an electrical transmission control which advantageously operates, when the speed regulation or speed limiting is active, on the basis of the engine torque setting produced at the torque level on the output side of the speed regulation or speed limiting stage. For this purpose the engine torque setting is transformed by a characteristic stage which is the inverse of the torque characteristic stage, to a transmission control preset signal at the level of the operating variable of the engine operation preset control element. When speed regulation and speed limiting are inactive, the transmission control preset signal is supplied in a conventional manner directly from the operating signal for this control element (that is, always at the engine power level) in every case.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.